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Psyche 5:79-84, 1888.

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THE MEANS EMPLOYED BY BUTTERFLIES OF THE GENUS BASILARCHIA FOR THE PERPETUATION OF THE SPECIES. BY SAMUEL HUBBARD SCUDDER, CAMBRIDGE, MASS. The power of reproduction conceded,
the universal instinct for self-preserva- tion is the fundamental and controlling
principle by which the perpetuation of
any kind of animal is successfully
reached. The uncontrollable m:iternal
instinct of self-sacrifice existing in some animals alone overmasters it, and this
exists only in the higher zinimals, which, compared with the great mass, are but
few in number; and is then in most
cases called into play only when the
creature's life-work is nearly finished. No such instinct occurs among butter-
flies, nor is in any way likely to be
found, so that uself-preservation" and
"perpetuation of the species" are here.
at least through all but the closing days of life, practically equivalent terms.
The "struggle for existence" in the
species and in the individual are largely convertible terms.
This struggle is the perpetual inheri-
ance of the individual. The individual
inherits alike its structure and its habits of life, which latter are very largely,
perhaps almost absolutely, dependent
on its structure ; its tastes and its pro- pensities, its fears and its devices to cir- cumvent its enemies; all its instincts,
which are to a great extent, possibly
wholly, the entailment of ancestral
habits ; its very attitudes, whether at
rest or in motion. Its advantages and its disadvantages are thus alike its legacy ; so too the peculiar means it employs to
disembarrass itself of these disaclvan-
tages. This is especially and more
immediately true of the insect in its
earlier stages, where freedom to change
the immediate sun-oundings is exceed-
ingly limited or altogether impossible,
except so far as theie is foresight, or an instinct marvello~~sly akin to foresight on the part of the creature in an antece- dent stage.
It is of more than usual interest to
study the means of self-preservation in
the genus Badarchia, since there is
haidly anotlie~ genus of butterflies
where throughout its entire life the in- sect is apparently so exposed to its
enemies. They are all, of their kind,
conspicuous objects even to our dull
eyes, and mole than that they are, with
the exception of the chrysalis, always
found in unusually conspicuous situa-
tions. How then do they manage to
escape their keen sighted foes, the birds, or their wakeful, indefatigable. persis- tent enemies among the insect tribes,-
ichneumons, ants, wasps, flies, mites,
and spiders?
Take first the egg-stage.
Every one
who has attempted to rear butterflies
knows what immense destruction falls
to the lot of any species at this stage in its life. Ants and spiders look on them
as delicacies made for their delectation, and there is a whole group of tiny
Pu&e 5 079-85 (pre.1903). hfp //psyche aitclub org/5/5.0079 htd



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[ July-August 1888.
hymenoptera, almost too small to
breathe, one would think, mere specks,
which live solely upon insects' eggs,
piercing them with their egg-darts,
their progeny living imprisoned and
feeding on the contents until they have
run the cycle of their changes. Some
attack whole batches of eggs, laying
one egg in each, so that one parasite
may destroy the entire brood of one
butterfly ; others lay their all in one or two eggs,
and it is to this class that
those belong which sting the eggs of
Basilarchia. How does Basilmchia
escape this danger? In the first place,
the mother rarely lays more than
one egg in one spot or even on one
bush, though as many as a dozen or two
may occasionally be found, where the
butterfly's numbers are great and they
are growing as it were imprudent.
Then it must be remembered fii st that
-to judge from the latest researches-
these pa.i\isitic flies must be guided less by vision than by touch ; and second,
that most insect eggs are laid on the
broader parts of the leaf on which the
young will feed ; it is here that the
parasite will range in quest of prey ;
but the eggs of Badarchia are rarely
found except at the extreme tips of
leaves, and in addition the leaves of the food-plants concerned are all acuniinate, someto an excessive extent, as in some
of the poplars and birches. When the
parasite has, however, found an egg, it
may well be inquired whether she
would not be deceived by it. It differs
from the eggs of all our other butter-
files; in thiit it is besprinkled with little flexible filaments for all the world like the hairs of some leaves. Or if the
clothing of the eggs did not deceive,
she might even then find it difficult of attack, for minute as these parasites are, less than half a millimetre long, their
bodies would extend across at least
three of the polygonal cells which regu- larly stud the surface of the egg, and
which send forth these little filaments at every angle, so that poor bewildered
madame must struggle through a weary
chappara1 before she can attain the bar- ren grounds at the summit and find a
spot to readily insert her sting. Yet
that she succeeds is only too evident to the collector; the larger part of the
eggs obtained in the open field which
have fallen into my hands have been
parasitized.
This is its but too partial defence
against its special enemies. But how
about those wandering buccaneers, the
ants, mites, and spiders?
These labor
under the same visual defects as the
direct parasites, or sometimes greater
ones, and the position of the egg, re-
mote from their usual hunting ground,
must serve as no inconsiderable protec-
tion ; how great, there are hardly means of measurement. Their greatest pro-
tection from these savages, which can-
not fly but must wander ceaselessly
about on foot in search of prey with
satanic energy, is undoubtedly in the
fewness of their number on one plant.
The spider that finds two
eggs of a
BasiIarchia in one day must be an ex-
cellent hunter.
Escaped at last from these dangers,




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July-August IS%.]
which only lasted at the most ten days
the caterpillar crawls forth from its
prison and begins its active life. It is a scrawny juiceless looking thing, all cov- ered with warts, and less than any other newly born caterpillar, would seem a
tempting morsel even to an ichneumon
or a spider. Yet both make havoc
with it at this time. To a wandering
ichneumon contact with an empty egg-
shell would probably mean, as a result
of its inherited wisdom, that some nice
young caterpillar was about, and the
neighborhood would be all the more
thoroughly ransacked. Caterpillars cle-
vouring their egg-shells, and so not
leaving this "scent" behind them,
would oftenest escape, and by degrees
this habit would be perpetuated and
fixed ; and so it is here ; almost invari- ably the caterpillar hastens to destroy its former prison walls, which it devours
to the very base, too closely glued to the leaf to be eaten; probably it breathes
more freely when that is done.
But where does it now find itself?
Its food at its very feet,-yes ; but in the most exposed position possible. Atop
the extreme tip of one of the out-
most leaves of a spray that projects
most freely into the sun and air, just
where it can most easily be seen by the
passer by ; this seems to be the case
nine times out of ten. It is, however,
probably the safest place from the
prowling spiders ; but surely not from
its flying enemies. What does it do?
retreat down the leaf? That would be
only to exchange one danger for an-
other, and on its way to a presumed
place of safety it would be more sure of detection, because a imovi'rg object in
nature is alway most easily noticed. No, it eats the nearest bit of leaf down to
but not including the midrib, first on
one side and then on the other, and then retires to near the tip of the midrib to digest it ; subsequent meals it takes in the same way, moving with excessive
deliberation along its narrow path and
retiring always to the same spot. On
this perch it cannot be seen from below, :iiicl from the sides and above seems
almost or wholly a part of the denuded
midrib to which it clings ; more partic- ularly when the leaves are in motion by
the wind, as they usually are on the
trees on which it feeds, particularly in the case of the aspen.
That this mode of life is on the whole
an advantage to it is rendered probable
from the fact that there are two cases
known, in which it is followed very
closely by caterpillars of a moth (Noto- donta), feeding on the very same plant
as species of butterflies with this habit (one in Europe and one in America) ;
while the caterpillars of Basilarchia
employ a further device, the actual im-
port of which has been a puzzle. Very
soon after birth, when it has eaten but
a very few swaths down the leaf, the
little fellow constructs a small and loose packet from minute bits of leafand other rejectamenta, loosely fastened to one
another and to the midrib, close to but
scarcely touching the eaten edge of the
leaf, and as fast as the leaf is eaten, it removes this packet (continually added
to until it becomes about as big as a




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82 PSYCHE. [~uly-~ugust ISSS.
small pea), farther and farther clown the midrib away from its perch, always
keeping it near the eaten edge. It should be noted that it is so loosely attached, the bits of leaf at all possible angles, that it is moved by the least breath.
Meanwhile the caterpillar has been
growing larger and more conspicuous
and thus in greater peril from its ene-
mies. There are two possible services
that this odd packet may render. A
spider wandering over the leaf and ob-
serving its motion may seize it and think- ing it has a prize hurry away with it
and leave its architect unharmed. This
seems to me rather a strained sugges-
tion, for a wandering spider would
probably proceed to investigate it. on
the spot. Another explanation seems
more probable. It should be I-emem-
bei-ed that the leaves preferred by these creatures as food are mostly such as are easily shaken by the wind, and as the
caterpillar moves with the leaf and with all the surrounding leaves, in a contin- ual fluttering in the case of the trembling aspen, and to a less degree in the other food-plants, this of itself is a protection to it. as it would more readily escape
observation as an object distinct from
the leaves, all being in motion together ; but on the more stable leaves like the
willow and especially the Rosaceae and
the oaks, the motion in a feeble wind
would not be sufficient to be serviceable, and here at least the packet comes into
play. An object in motion among
others at rest is a most noticeable thing, n. fact well recognized among animals,
as a host of them show when they fear
being seen.
This packet attached by
loose silken threads moves, as stated,
with a breath of wind and so would dis-
tract attention from its architect near by, who has taken pains to place it at the
farthest remove from its perch, while
still (to avoid undesirable steps) on its daily track. If this be really its object, it is surely one of the oddest devices in nature.
The species of Basila~chia all pass
the winter while in the caterpillar state and but partly grown. The caterpillar
has moulted at least once (devouring
its cast-off clothing, by the way, doubt- less that it may not attract attention)
and has to prepare against the
incle-
ment season.
This it does in a very
shrewd way, which is all the more re-
markable because no trace or semblance
of it is seen in caterpillars of the broods that attain their entire growth in the
same season. When the proper time
approaches, warned thereto possibly by
the dryness of its food, or by the cooler nights, the caterpillar constructs a little nest, sometimes from the still unfinished leaf on which it was born, sometimes
from one which it prepares specially at
greater pains; this is done by eating
away or biting off the unnecessary parts, and leaving on either side of the base of the leaf little flaps just large enough, when drawn together, bottom side up
and meeting above, to form a cylinder
into which it can squeeze; a project-
ing shelf is also left beyond the open-
ing, on which it may stand when ready
to crawl in, and upon which it may
back out in the spring ; the whole




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~uly-~ugust 1~88.1 PSYCHE. 83
of the inside and the upper s~n'face of
the shelf are then plastered over with a dense coating of brown silk and the
flaps drawn together; more than that,
with strangest foresight. the petiole of the leaf is thoroughly fastened to the
stem by numberless threads passed
carefully and tightly around both ; into this cylinder it then crawls head fore-
most, completely filling the cavity,
closing the bevelled hinder opening
with the sloping tubercula te and sharp- ened terminal segments, sure to find
itself there when the 1011g night of winter is passed. No, not quite sure, for wasps or some other strong predaceous insects
will tear this fine castle open and
destroy its single occupant. Whether
it is an additional safeguard or not, it is an instructive fact that, at least where the winters are most severe, nearly all
these hibe1 nacula are made out of leaves so near the ground that the snow covers
them with its warming mantle ; and
what is more, in certain cases they so
closely resemble the winter buds and
bursting leaves of the new year that
they must sometimes deceive their
prowling foes of the early spring.
Shortly after it appears again in the
spring and has fed on the tender buds
and just opening leaves, it moults
again, usually upon the shelf of its
hibernaculum but no longer devours its
skin, as it quits the immediate neigh-
borhood. It now changes its livery as
well and is a most extraordinary look-
ing object, withal very conspicuous.
Dark and light green and cream color
strive for the mastery ancl leave it
streaked ancl blotcl~ed so that it bears no inconsiderable resemblance, in color at
least, to the droppings of some birds, a circumstance which doubtless serves it
as some sort of protection. Its body is
bumped and the bosses bear tubercles
which give it a somewhat repulsive as-
pect ; especially a pair a little behind the head are raised aloft thickly studded with prominences, the effect of which
is heightened by the creature's habit of arching this part of the body. bending
its head to the ground and raising aloft its hinder part, also studded wit11
roughened processes. Altogether it is
Ì rather hideous beast. Then too, if
disturbed, it raises the front half of its body from the ground and uses it as a
kind of whip-lash throwing it to one
side and the other with great violence.
When it walks it moves with a slow
and cautious tread, its head trembling
as if it had the palsy. All this is doubt- less to inspire fear to such enemies as. might he tempted to attack it, but to
how in~~cli avail we can hardly tell. Tt is certainly attacked in considerable
numbers by a parasitic l~yinenopteson,
the yonng of which live within on the
juices of the body and escape from the
chrysalis when that is formed.
The chrysalis, helpless thing, proba-
bly hangs quite exposed upon the stem
of the plant which has given the cater-
pillar nourishment. We know it almost
entirely from those raised in confine-
ment. It has an oddly shaped form
with a great projection on the back like a Roman nose, and is of a dark green
or greenish brown color varied with




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cream color, and smooth as if varnished. Tliis makes it appear like a hanging
lump of bird dung, and so again must
often prevent its being picked off and
devoured by some hungry bird.
When one that has at last escaped all
the perils of its youth finally reaches its full development, it is even more con-
spicuous and exposed than before. AL
though now upon the wing and 110
doubt often able to escape a pursuer by
some quick movement, its natural flight
is not swift, and its ordinary movements on the wing are :i few quick flutters
followed by a sailing motion which is
most fiivorable to ~iipt~ire. Its colors differ of course in the different kinds, and they may in this particular be di-
vided into two classes. One affects a
deep rich black blue or blackish purple, and is variegated with light blue and
white, the latter partly in the form of
bands, on some forming a broad bow
across both wings, rendering them
most conspic~io~is and striking objects. They are, too, of a pretty large size,
and as they fly mostly in the neighbor-
hood of copses or along shaded road-
sides or forest roads, they seem to
render themselves by the contrasting
back-ground as conspicuous as possible.
Another class is of an orange brown
color of greater or less depth, while the veins are black, and a black stripe,
sometimes accompanied by white dots,
crosses the wings. These fly in more
open places, more fully exposed to the
SLIII and are scarcely less conspicuous
thtin their fellows. All these butterflies live a considerable time, and indeed the eggs do not mature in the bodies of the
females until they have been a fortnight on the wing ; and then they do not lay
all their eggs at once, or even within a few days, but prolong the operation
over many days or even several weeks.
To deposit all her eggs therefore, which is the province of course of the female, she must fly amid all the dangers her
conspicuous colors ones for about a
month, a considerably longer time than
the average of butterflies. Previous to
egg-laying at least, much of her time is spent upon the ground in company with
her fellows, often in great flocks. en-
grossed in sucking up moisture from the
damp earth, from decaying fruits or the
droppings of beasts; and so must be-
come a conspicuous and easy prey to
her enemies.
What then is to become of this saving
remnant of the tiibe? How escape